Absorbent single use hygiene item

ABSTRACT

The invention concerns an absorbent single use hygiene item comprising a liquid-tight back sheet ( 4 ) and a liquid permeable cover sheet ( 2 ), with an absorbent body ( 6 ) containing super-absorbent polymer materials and suitable for storing bodily fluids, especially urine, which is disposed between the back sheet ( 4 ) and the cover sheet ( 2 ), and with a two-ply intermediate layer ( 8 ) which takes up and distributes liquid. The intermediate layer ( 8 ) is made from a top stratum ( 18 ) consisting of synthetic fibers and a bottom stratum ( 20 ), the average pore volume of the top stratum ( 18 ) being greater than the average pore volume of the bottom stratum ( 20 ), and is disposed between the absorbent body ( 6 ) and the cover sheet ( 2 ). The hygiene item in accordance with the invention is constructed in such a fashion that the bottom stratum ( 20 ) consists essentially of chemically cross-linked cellulose fibers and the longitudinal end sections ( 19 ) the top stratum ( 18 ) overlap the longitudinal ends ( 21 ) of the bottom stratum ( 20 ) so that the hygiene item can absorb repeated liquid discharge and gives the wearer a feeling of dryness. The cross-linked cellulose fibers of the bottom stratum ( 20 ) are also more hydrophilic than the synthetic fibers of the top stratum ( 18 ).

BACKGROUND OF THE INVENTION

The invention concerns an absorbent single use hygiene item having aliquid tight back sheet, a liquid permeable cover sheet, an absorbentbody comprising a suitable super absorbing polymer material (SAPmaterial) disposed between the cover and the back for absorbing bodyfluids, in particular urine, and with a liquid absorbing intermediatelayer comprising a top stratum (18) made from synthetic fibers and abottom stratum (20), wherein the average pore volume of the top stratum(18) is larger than the average pore volume of the intermediate layer(8) bottom stratum (20) and wherein the intermediate layer (8) isdisposed between the absorbent body (6) and the cover sheet (2).

A hygiene item of this kind has been disclosed in DE 92 18 991 U1. EP 0689 818 A2 discloses a hygiene item with which the intermediate layer ismanufactured together with the absorbent layer using a multi-layer flatmaterial comprising a liquid tight back sheet, a cover sheet which ispermeable to liquids, and an absorbent body containing a super-absorbentpolymer material and disposed between the sheets which is suitable forthe storage of body liquids, in particular urine. A two-ply liquidabsorbing and distributing intermediate layer consists essentially of atop stratum made from synthetic fibers and a bottom stratum, wherein theaverage pore volume of the top stratum is larger than the average porevolume of the bottom stratum. The intermediate layer is disposed betweenthe absorbent body and the cover sheet.

Hygiene items, in particular diapers or incontinence inlays, containingSAP materials in their absorbent body are susceptible to so-called gelblocking. The SAP materials swell in the region of liquid discharge toimpair additional liquid acceptance in particular in response torepeated liquid discharge in these regions. The intermediate layerdisposed between the cover sheet and the absorbent body is therebyintended to act as a kind of intermediate buffer for absorbing theincident liquid, for distributing the liquid within intermediate layer,and for passing the liquid into the absorbent body. Liquids in thevicinity of liquid discharge can thereby be transported to remotelocations of the absorbent body or to SAP materials contained thereinwhich are still present in an “unused” state.

WO 91/11162 discloses a hygiene item having a liquid acceptance anddistribution layer located above the absorbent body and comprisingcross-linked cellulose fibers.

The chemical cross-linkage of the cellulose molecules is present withinthe cellulose fibers through cross-linkage of the cellulose moleculeswithin a single fiber only and is not active between fibers. Inconsequence thereof, these fibers are relatively stiff, textured, andelastic. The intramolecular absorption capacity of the fibers isreduced. Such fibers are better suited for processing repeated dischargeof liquid streams than are the non-chemically cross-linked cellulosefibers of the absorbent body. They are better suited for rapidabsorption, containment, internal distribution and passage thereof tothe absorbent body. In addition to the chemically cross-linked cellulosefibers, the intermediate layer of the conventional hygiene item containsa thermoplastic bonding material in the form of an admixture ofthermoplastic fibers. Heating of the fiber mixture leads to melting ofthe thermoplastic fibers and to glue-like mutual bonding and securing ofthe chemically cross-linked cellulose fibers. This is reported as beingparticularly advantageous.

EP 0 397 110 A1 describes a diaper having a synthetic fiber-based,voluminous bonded fiber fabric which is disposed as an intermediatelayer between the absorbent body and the cover sheet to providetemporary liquid absorption. The layer must however have an area densityof at least 60 g/m² for adequate intermediate storage and distributionof the discharged liquid. Materials used in the voluminous, bonded fiberfabric layer are expensive, create logistic problems, and are difficultto integrate into high speed machinery, since a continuous roll of thismaterial having finite, conventional usable diameter can only have avery limited working length and frequent exchange of the rolls isnecessary.

Departing from the above described prior art, it is the underlyingpurpose of the invention to create a hygiene item having a high fractionof super-absorbing polymer materials in the absorbent body whose storagecapacity can be better and more completely used than that of the hygienearticle disclosed in WO 91/11162. In addition, the hygiene item must beinexpensive to produce. Departing from the hygiene item categorizing theinvention, it is the underlying purpose of the present invention tocreate a hygiene item of simple construction which is thereforeinexpensive to manufacture, whose liquid absorption performance andwhose liquid storage performance is improved, in particular, in responseto repeated application of liquids. The hygiene item user should alsonot feel the liquid remaining in the intermediate layer, e.g. as aresult of body weight pressure on the skin following repeated liquiddischarge.

SUMMARY OF THE INVENTION

This purpose is achieved in accordance with the invention with a hygieneitem of the above mentioned kind, wherein the bottom stratum is madefrom chemically cross-linked cellulose fibers and the longitudinal endsections of the top stratum overlap the longitudinal ends of the bottomstratum, with the hydrophilicity of the chemically cross-linkedcellulose fibers of the bottom stratum being larger than that of thesynthetic fibers of the top stratum.

In accordance with the invention, the lower stratum of the intermediatelayer is made solely from chemically cross-linked cellulose fibers. Thegood performance of the two stratum intermediate layer constructed inaccordance with the invention results from a synergetic interactionwhich can be explained as follows. The gradient of the average porevolume (as seen in a direction towards the absorbent body, perpendicularto the plane of the cover sheet) initially provides a relativelylarge-pored liquid acceptance volume for liquids incident on the topstratum of the intermediate layer. The liquid can then gain access intothe absorbent body via the bottom stratum of the intermediate layer. Thereduced hydrophilicity of the synthetic fibers in the top stratum of theintermediate layer compared to that of the chemically cross-linkedcellulose fibers of the bottom stratum of the intermediate layer and, inaddition, its preferentially lower hydrophilicity compared to thenon-cross-linked cellulose fibers of the absorbent body, support thedesired direction of liquid transport. The bottom stratum of theintermediate layer made from chemically cross-linked cellulose fibershas a certain liquid guidance capacity due to the capillary absorptionaction of the fibers so that liquids passing through the top stratum ofthe intermediate layer and into the bottom stratum are distributedthrough the plane thereof into regions removed from the point of liquidincidence for further transport into the underlying absorbent body atthese locations. Following repeated discharge of liquids, the storagecapacity of the absorbent body is nevertheless nearly exhausted in theregions at which liquids are incident. This point in time is criticalfor the function of the hygiene item. The bottom stratum of theintermediate storage layer can then store additional incident liquid, atleast to a limited extent. This storage capacity is effected by theremaining molecular bonding capacity of the cross-linked fibers and bythe pore volume remaining between the fibers. The bottom stratum of theintermediate layer thereby provides reserve storage capacity. The amountof liquid stored therein which is pressed out to the surface of thediaper, i.e. to the skin of the diaper user, is thereby substantiallyreduced, since the upper large pore stratum of the intermediate storagelayer has synthetic fibers with reduced hydrophilicity and thereforefunctions as a spacer. The synthetic fibers of the top stratum of theintermediate layer preferentially have very reduced hydrophilicity andtherefore do not allow for substantial molecular bonding of liquids.This layer therefore remains essentially dry.

The overlap of the longitudinal end sections of the top stratum of theintermediate layer with the longitudinal ends of the bottom stratum ofthe intermediate layer reliably prevents liquids which may be present inthe bottom stratum of the intermediate layer from being pushed to thesurface of the hygiene item.

The edges of the longitudinal end sections of the top stratumadvantageously lie within the absorbent body, i.e. at a separation fromthe longitudinal ends. The storage capacity of the absorbent body canthereby be better utilized. For the above mentioned case of repeatedliquid discharge, the storage capacity of the absorbent body isexhausted in the region of incidence thereof and the bottom stratum ofthe intermediate storage layer assumes its reserve storage function totransport additional incident liquid at the border between the twostrata of the intermediate storage layer or in the lower region of theupper stratum of the intermediate storage layer. The liquid is reliablypassed into the absorbent body when it reaches the longitudinal ends ofthe bottom stratum of the intermediate layer, assuming that the storagecapacity of the absorbent body has not yet been exhausted in thisregion.

In accordance with a preferred embodiment, the above mentioned liquidtransport in the lower region of the top stratum of the intermediatelayer can be improved when the top stratum has a pore volume whichdecreases in the direction of liquid transport from the cover sheet tothe absorbent body, i.e. perpendicular to the plane of the layer. Thepore volume must not decrease in a discrete manner from a larger valueto a smaller value, rather can decrease in a quasi-continuous fashion ina downward direction within the top stratum of the intermediate layer.

The intermediate layer is preferentially constructed in such a fashionthat the fibers of the top stratum engage into the bottom stratum tothereby form a transitional zone between the strata. The fibers in thebottom stratum can correspondingly engage into the absorbent body sothat a transitional zone is also formed between the intermediate layerand the absorbent body.

The above described two-ply construction for the intermediate layer andthe function of the bottom stratum thereof facilitate a low surfacedensity for the top stratum, preferentially less than 55 g/m². Thispermits preparation of a continuous roll of materials used thereforhaving, from a manufacturing point of view, a satisfactory, largeworking length so that the material can be integrated into high speedmanufacturing equipment.

The top stratum of the intermediate layer is preferentially made from abonded fiber fabric which is more voluminous than the bonded fiberfabric of the cover sheet. A large number of conventional syntheticfibers are known to one of average skill in the art as are methods forthe manufacture of bonded fiber fabrics and further description thereofis unnecessary. The bonded fiber fabric preferentially comprisesconventional two-component fibers e.g. of the cladded core type. A fiberfabric can thereby be conventionally, thermally processed into aconsolidated bonded fiber fabric without damaging the fiber structure.Two-component fiber thicknesses of at least 4 dtex and preferentiallybetween 5 to 8 dtex have turned out to be advantageous. In this manner,the titer of the fibers is sufficiently large to give the bonded fiberfabric the desired pore volume, even following thermal compacting.(Thick fibers cannot be packed and volume-filled to the same extent asthin fibers). One of average skill in the art is also aware of means foradjusting the hydrophilicity of synthetic fibers so that furtherdiscussion thereof is not needed here. Using such techniques, thepreferentially very low hydrophilicity of the top stratum of theintermediate layer can be substantially reduced to, in any event, besignificantly lower than that of the chemically cross-linked fibers ofthe bottom stratum. The absorbent body below the intermediate layer isadvantageously double-layered, with the upper layer thereofsubstantially containing cellulose fibers and super-absorbing polymermaterials and the lower layer consisting essentially of cellulose fibersonly. An optimized use of the absorption capacity of the absorbent bodyis thereby effected.

Further advantages, details and features of the invention can be derivedfrom the accompanying patent claims and drawings as well as from thesubsequent description of a preferred embodiment of the invention.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 shows a schematic view of the structure of a hygiene item inaccordance with the invention, and

FIG. 2 shows a longitudinal cut in the plane designated by the arrowsII—II.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The figures schematically show the structure of a hygiene item in theembodiment of a diaper. The diaper comprises a cover sheet 2, a liquidtight back sheet 4 and an intermediate absorbent body 6. A two stratumintermediate layer (designated in its entirety with reference symbol 8)is disposed between the cover sheet 2 and the absorbent body 6. In theembodiment shown, the cover sheet 2 extends in a longitudinal direction10 of the diaper to longitudinal edges 12 thereof and, in the transversedirection 14, up to the sideward transverse edges 16 of the diaper. Theliquid permeable cover sheet 2 is connected to the back sheet 4 alongand proximate to the longitudinal edges 12 and the transverse edges 16using arbitrarily conventional joining techniques. An embodiment is alsoconceivable with which the cover sheet 2 ends at a separation from thetransverse edges 16. Additional e.g. bundling elements or stretchingmeans can then be disposed past the cover sheet 2.

The two-ply intermediate layer 8 comprises a top stratum 18 and a bottomstratum 20. In the longitudinal direction 10, the longitudinal endsections 19 of the top stratum 18 overlap the longitudinal ends 21 ofthe bottom stratum 20 but end at or at a separation from thelongitudinal ends 22 of the absorbent body 6. The top and bottom strata18 and 20 have the same width in the transverse direction 14. The topstratum 18 can also advantageously overlap with the bottom stratum 20 inthe transverse direction.

The top stratum 18 is formed from a bonded fiber fabric made fromsynthetic fibers. A fraction of two-component fibers is preferentiallyused therefor. The bonded fiber fabric is compressed during manufacturein such a fashion that the top stratum 18 has a pore volume whichdecreases in the direction of arrow 24 of FIG. 2, i.e. in the directionof liquid transport, transverse to the planar extension of theintermediate layer 8.

The bottom stratum 20 consists essentially of chemically cross-linkedcellulose fibers. The pore volume of the bottom stratum 20 is lower thanthat of the top stratum 18 of the intermediate layer 8. Thehydrophilicity of the chemically cross-linked cellulose fibers of thebottom stratum 20 is also larger than that of the synthetic fibers inthe bonded fiber fabric constituting the top stratum 18.

When the liquid acceptance capacity of the absorbent body 6 is exhaustedin the region of liquid discharge following large amounts of incidentliquid, the intermediate layer 8 assumes a liquid storage and transportfunction. Renewed streams of liquid are briefly absorbed in therelatively large pored volume of the top stratum 18 and then passed tothe bottom stratum 20 of the intermediate layer 8, wherein theintermediate layer 8 thereby performs a storage function. When thestorage capacity of the bottom stratum 20 is also exhausted, liquidtransport occurs in the plane of flat extension of the strata at theborder region between the top stratum 18 and the bottom stratum 20.Liquid is thereby transported away from its location of incidence andpassed to non-exhausted portions of the absorbent body 6 still havingremaining storage capacity.

I claim:
 1. A single use absorbent hygiene article comprising: aliquid-tight back sheet; a cover sheet permeable to liquids; anabsorbent body disposed between said back sheet and said cover sheet,said absorbent body containing a super-absorbent polymer for absorbingat least one of body liquids and urine; a top layer disposed betweensaid absorbent body and said cover sheet, said top layer containingsynthetic fibers and having a first average pore volume and a firstaverage hydrophilicity; and an intermediate layer disposed between saidtop layer and said absorbent body, said intermediate layer consistingessentially of chemically cross-linked cellulose fibers and having asecond average pore volume which is smaller than said first average porevolume and a second average hydrophilicity which is greater than saidfirst average hydrophilicity, wherein said top layer has longitudinalend portions which extend past edges of said intermediate layer todirectly contact said absorbent body.
 2. The hygiene item of claim 1,wherein said longitudinal end portions of said top layer contact saidabsorbent body at a defined separation from longitudinal ends of saidabsorbent body.
 3. The hygiene item of claim 1, wherein said top layeris made from a bonded fiber fabric containing two component fibers. 4.The hygiene item of claim 3, wherein said two-component fibers have afiber thickness of between 5 to 8 dtex.
 5. The hygiene item of claims 3,wherein said two-component fibers have a fiber thickness of at least 4dtex.
 6. The hygiene item of claim 1, wherein said top layer has a massper unit area of less than 55 g/m².
 7. The hygiene item of claim 3,wherein said top layer has a mass per unit area of less than 55 g/m². 8.The hygiene item of claim 1, wherein said intermediate layer contains noSAP material.
 9. The hygiene item of claim 1, wherein said secondaverage pore volume is larger than a third average pore volume of saidabsorbent body.
 10. The hygiene item of claim 1, wherein said firstaverage pore volume decreases in a perpendicular direction towards saidintermediate layer.
 11. The hygiene item of claim 10, wherein said toplayer has an upper portion and a lower portion, wherein a pore volume ofsaid upper portion is larger than a pore volume of said lower portion.12. The hygiene of claim 1, wherein fibers of said top layer engage intosaid intermediate layer to form a first transitional zone between saidtop layer and said intermediate layer.
 13. The hygiene item of claim 1,wherein fibers of said intermediate layer engage into said absorbentbody to form a second transitional zone between said intermediate layerand said absorbent body.
 14. The hygiene item of claim 1, wherein saidabsorbent body comprises an upper portion consisting essentially ofcellulose fibers and super-absorbing polymer and a lower portionconsisting essentially of cellulose fibers only.